Information is processed along several parallel channels in the primate visual system. Some of these channels have been amply characterized with physiological and anatomical methods. In spite of this, at present we have only limited knowledge of the functions of these channels and why they have emerged in the course of evolution. The purpose of the proposed work is to obtain new evidence as to the function of two sets of channels in the visual system, the ON and OFF channels and the color-opponent and broad- band channels. To accomplish our aim, we have developed methods which allow us to reversibly or permanently inactivate some of these channels at various levels in the visual system using either pharmacological agents or lesions. Employing a combination of physiological and psychophysical methods we can then proceed to determine the neural responses and the visual capacities of monkeys while their visual system is intact or while one of the channels is blocked. The physiological methods we use are the electroretinogram and single-unit recordings in various parts of the visual system. The psychophysical methods we use involve training animals on a variety of detection and discrimination tasks allowing us to obtain reliable measures of the following visual capacities: color and luminance contrast sensitivities, stereopsis, acuity, pattern perception, motion perception and flicker sensitivity. Central to this effort is our ability to obtain psychophysical functions for specific retinal locations which we believe is an essential requirement for this kind of work. The findings of this research on the neural mechanisms of vision should provide significant new hints about the nature, cause and locus of visual deficits in patients, especially as it pertains to binocular vision where defects are most common in our society.